The present invention relates to a device for coupling a CB antenna to both a CB transceiver and to an AM-FM receiver.
In mobile units such as automotive vehicles it is common to have an AM-FM radio and a CB transmitter-receiver(transceiver). In such units it is common practice to provide one antenna for the AM-FM radio and a second separate antenna for the CB transceiver. One problem has been that a CB antenna system, including connecting coaxial cable, is normally unsuitable for the AM-FM receiver and vice versa. In the present invention a splitter circuit has been provided in which a CB antenna can be used with both a CB transceiver and an AM-FM receiver.
The frequency range for Class D CB operation is between 26.965 and 27,405 40 channel band MHz while FM is 88-108 MHz and AM is 540-1600 KC. In the present invention the CB antenna is connected to a coaxial lead line, having an impedance usually utilized for the AM-FM receiver. That coaxial lead line is connected to the AM-FM receive via a parallel LC trap, having a resonant frequency of 27.2 MHz. The parallel trap provides a high impedance to CB signals and low impedance to AM-FM signals. The coaxial lead line is also connected to the CB transceiver via a series LC circuit, which will not be resonant at 27.2 MHz, but which has an inductance which offers a high impedance to FM signals and a capacitance which offers a high impedance to AM. The LC circuit will have a net capacitive or inductive reactance for a purpose to be described. Now the series, non-resonant, circuit offers a low impedance to CB signals and a high impedance to AM-FM signals, with a net reactive component. The net reactive component is selected to have a magnitude which when taken with the rest of the system provides characteristic impedance resulting in matching. In addition the series circuit is connected to the transceiver via a coaxial line, having an impedance usually used for the CB lead line. Thus the CB antenna system is modified to minimize what would otherwise be a significant impedance mismatch between CB antenna and the coaxial lead line. The result is a total CB and AM-FM system which can function with good performance characteristics while utilizing only a single, CB antenna. It is common to have the CB antenna which is resonant at a frequency midway in the CB range. In the present invention, however, the antenna may be slightly detuned to compensate for the other components of the combined system.
Therefore, it is an object of the present invention to provide a CB and AM-FM system and/or method utilizing a single, CB antenna.
It is another object to provide such a system and/or method in which a conventional AM-FM coaxial lead line can be used from the CB antenna.
It is another object to provide such a system and/or method in which a tuned resonant circuit is utilized to block CB signals from the AM-FM receiver and a series, non-resonant LC circuit is used to block AM-FM signals from the CB transceiver.
It is another object to provide such a system and/or method in which the series non-resonant LC circuit has a net reactive component of a preselected magnitude to compensate for lead line mismatch to the CB system.
It is another object to provide such a system and/or method in which the CB antenna may be slightly detuned to compensate for other components of the combined system.
It is another object of the present invention to provide an improved combined CB and AM-FM system and a system for implementing the same.